Welcome to COL.
The most important thing I found with training my cockers was focusing them. If they've got their noses on the ground all the time then they're not listening to you. I use treats, vocal commands ('what's this') and games to keep them focused, and making them work harder for treats as time goes on and then only reserving the high value treats for new stuff. The more you focus them the greater the bond you develop.
At 5 months she's still learning and some days will be better than others, and other days you find yourself revisiting the scene of a crime you visited before (what I'm saying is that at this age and possibly for the next 18 months don't expect that even though you think you've solved one problem it doesn't occur somewhere else along the line)! Some things you have to do in stages/parts before you can fulfil the thing you actually want to do. The bit I love about cockers is that they keep you on your toes. With patience and persistence you'll get there in the end (but you need a very good sense of humour), even though it may be a bit frustrating at times.
Can't you use a different command for trailing as I assume it doesn't matter what you call a command as long as you're consistent and your dog associates a command with any word you want to use.
